1. Field of the Invention
The present invention relates to an electronically controlled camera having a motor-driven film wind and rewind system, and more particularly to a camera having a memory unit for example, for storing a starter signal for causing its electronic control system to perform a predetermined operation.
2. Description of the Prior Art
With a known camera having a film wind and rewind system as noted above, in rewinding a film after the film has been wound to the end and a motor has stopped, a transmission changeover gear is caused to slide by a transmission changeover mechanism with the motor standing still, thereby to change a transmission system engaged by the changeover gear from a wind side to a rewind side.
However, a drive gear and the transmission changeover gear are in engagement with each other having respective teeth in contact when the film winding is completed. If the transmission system is switched in that state, the transmission changeover gear is moved through sliding contact with the drive gear and the resulting sliding resistance tends to impair a smooth switching of the transmission system.
Furthermore, well-known means for interrupting a picture taking action after the film has been wound to the end in the conventional camera comprises means to mechanically lock a pressure of a shutter release button when the end of the film is wound up, or means to detect an increase in resistance to the film winding at the end of the film to interrupt a shutter release operation.
However, although the above conventional means is effective to prevent a picture taking action, there is a problem in applying such means as it is to a camera having a light measuring device. That is, the light measuring device generally is operable in interlocked relationship with the shutter release button or a film winding device. Therefore, in the latter case where just the shutter release operation effected with the shutter release button is interrupted, the light measuring device will operate although the film has been wound to the end. This results in wasteful power consumption and an early exhaustion of batteries. On the other hand, the former case where the shutter release button is mechanically locked requires a mechanism for locking the shutter release button and an interlocking mechanism to enable a locking operation.
Furthermore, a known memory unit for the electronic control system in the conventional camera comprises operation means for performing a predetermined operation, a starter switch for starting the operation means, and memory means operable in response to closure of the starter switch to shift from a first state to a second state and remain in the second state, to output an operation signal to the operation means while in the second state, and to return to the first state in response to a signal output by the operation means at the end of its operation.
The principle of this conventional memory unit is, for example, as shown in FIG. 15A of the accompanying drawings. In this example, a starter switch S' for starting operation means C' is connected to a set input terminal S of a flip-flop FF' which is one example of memory means. This flip-flop FF' is set by closure of the starter switch S'. That is to say the flip-flop FF' shifts from the first state to the second state. The flip-flop FF' has an output terminal Q connected to the operation means C', and the operation means C' operates in response to a signal output from the output terminal Q in the set state. An output terminal of this operation means C' is connected to a reset input terminal R of the flip-flop FF'. The flip-flop FF' is reset upon receipt of a signal output from the operation means C' at the end of its operation. That is to say the flip-flop FF' returns to the first state.
Such a prior art construction as above, however, is prone to the following problems and has room for improvement.
When the starter switch S' is closed, an electric current flows through this switch S'. The current continues to flow through the switch S' while the switch S' is closed. Therefore, power tends to be consumed to a wasteful degree even though the operation means C' is operable only by setting the flip-flop FF' which is one example of memory means.
Particularly with a battery-operated camera or other instruments, battery sizes are often limited in the interest of compact designing. Since battery capacity is also limited, wasteful power consumption as noted above results in early exhaustion of the batteries.
Another example of known memory unit has the memory means shiftable from the first state to the second state by closure of a set switch, and further comprises output means operable in response to an operation permit signal resulting from closure of the starter switch after opening of the set switch to output an operation signal to cause the operation means to perform the predetermined function.
Such a memory unit is constructed as shown in FIG. 15B.
In this example, a set switch S' for starting operation means C' is connected to the set input terminal S of the flip-flop FF' which is one example of memory means, and an AND gate AN' which is one example of output means receives a signal indicating the state of the set switch S', a signal indicating the state of the starter switch E' and an output signal from the flip-flop FF'. IN1' and IN2' in the drawing denote inverters provided for conformity of the logic.
This flip-flop FF' is set by closure of the set switch S' and its output signal changes to "H" level. In other words, the flip-flop FF' shifts from the first state to the second state and outputs an operation permit signal. If in this state the starter switch E' is open, the operation means C' will not operate yet. When the set switch S' is opened, the signal indicating the state of this switch S' changes to "H" level. The input to the flip-flop FF' changes to "L" level but its output remains in "H" level. When in this state the starter switch E' is closed, all the inputs to the AND gate AN' change to "H" level and the operation signal is output to the operation means C' whereby the predetermined operation is carried out.
An output terminal of this operation means C' is connected to a reset input terminal R of the flip-flop FF'. The flip-flop FF' is reset upon receipt of a signal output from the operation means C' at the end of its operation. That is to say the flip-flop FF' returns to the first state.
However, the above prior art construction is prone to the following problem as is the preceding example, and there is room for improvement.
That is to say, when the set switch S' is closed, an electric current flows through this switch S'. The current continues to flow through the switch S' while the switch S' is closed, and hence a great power consumption.
Furthermore, such a memory unit memorizes the closure of the set switch S' even when the starter switch E' is open, and the predetermined operation is carried out only when the set switch S' is closed and then opened and in that state the starter switch E' is closed. Therefore, the set switch could inadvertently be kept closed over a long period of time. As a result power could be consumed to an wasteful extent during this time. Thus, this prior art construction, like the preceding example, is unsuitable for a camera or the like instruments.